NUTRIENT ENRICHMENT OF SWEET POTATO (Ipomoea batatas L.) BY SOLID SUBSTRATE FERMENTATION USING FOUR FUNGAL SPECIES

Sweet potato (Ipomoea batatas L.) tubers and flour were fermented using pure strains of four fungal species: Aspergillus niger, Rhizopus stolonifer, Neurospora sitophila and Saccharomyces cerevisiae using solid substrate fermentation at 300C for 72 hrs. The protein content of the samples increased significantly (p£0.05) from 2.34±0.07% in the unfermented tuber to values ranging from 11.46±0.01 and 12.62±0.09% in the fermented tuber and 6.26±0.05% in the unfermented flour to values ranging from 7.83±0.06 and 9.70± 0.02 in the fermented flour. Fat content was also increased in the fermented tubers. However, fermentation decreased the fat content of the flour except in Aspergillus niger- fermented flour. Fermentation increased the ash content of the samples (except in Saccharomyces cerevisiae- fermented tuber, Rhizopus stolonifer-fermented flour and -fermented flour). The crude fibre, carbohydrate, sugars (reducing, non-reducing and total) and starch contents of both flours and tubers reduced after fermentation. Mineral elements such as Mg (except in Saccharomyces cerevisiae fermented tuber and Aspergillus niger fermented tuber), Ca (except in Aspergillus niger - fermented tuber), P (except in Rhizopus stolonifer fermented flour), and K (except in Aspergillus niger fermented flour) and decreased significantly; while Zn (except Saccharomyces cerevisiae fermented tuber and flour and Aspergillus niger fermented flour), Fe (except in Saccharomyces cerevisiae ferment tuber and flour and Rhizopus stolonifer fermented tuber) and Na (except in Rhizopies stolonifer fermented tuber) contents increased. Overall, Aspergillus niger appeared to be the most nutritionally-enriching compared to other fungi, while the sweet potato tuber proved to be a better fermentable substrate than the flour. KEY WORDS: Fungi, Nutrient enrichment; Solid substrate fermentation; Sweet potato. Global Jnl Pure & Applied Sciences Vol.10(1) 2004: 31-3